This invention relates to a sealing arrangement for a shaft rotatably mounted in a housing and which operates in an abrasive media, such as shafts for ship drives and the like. More particularly, the invention relates to sealing arrangements of the type having a main seal and an auxiliary seal fitted around the shaft, and with a chamber between the seals delimited by housing and shaft parts, which chamber is filled with a pressurized medium.
Sealing arrangements of this type are known, and are used, for example, in ship construction for sealing the tail shaft in the stern tube. The known sealing arrangements comprise a hollow space filled with pressure oil between an outer auxiliary seal in contact with the water, said seal generally being in the form of a shaft seal, and an inner main seal, which can be provided, for example, with a plurality of main shaft seal sections. The purpose of the auxiliary seal consists in preventing contact between harmful substances such as sand or the like and the main seal for as long as possible. Such harmful substances could gradually destroy the main seal and such auxiliary seals are intended to achieve the longest possible maintenance intervals. The filling of the hollow space between the seals with pressure oil also serves, in the event of a loss or decrease in the sealing action of the auxiliary seal, to avoid the penetration of water in the direction of the main seal. The oil supply in the hollow space must therefore be monitored and topped up from time to time. The disadvantage of this arrangement is that pressure oil escapes toward the water side through the auxiliary seal, if the auxiliary seal is adversely affected by the use especially of abrasive media, so that environmental pollution cannot be avoided.
On the other hand, an object of the invention is to provide an improved sealing arrangement which operates in a more environmentally safe and operationally reliable manner.
This object is achieved by providing that the chamber intermediate the main and auxiliary seals is continuously connected by a feed opening with an environmentally harmless separating medium under pressure and is provided with an outlet opening for the separating medium, the pressure of the separating medium and the dimensions of the feed opening and outlet opening are so adjusted to one another that a certain amount of separating medium escapes through the auxiliary seal. By using a separating medium which is continuously supplied into the hollow space, which medium is compressed air in an especially advantageous preferred embodiment, and by using the design according to the invention, a continuous sealing pressure is maintained in the hollow space which can serve on the one hand to press the main seal firmly against the parts to be sealed and on the other hand can serve to largely prevent the penetration of abrasive media, for example, sand, through the auxiliary seal. Since an outlet opening is also provided, pollutants which are in the hollow space can be continuously flushed from the latter. The space in front of the main seal is thereby kept free of contamination, and the main seal itself can enjoy a longer service life.
The flushing effect of the hollow space can be improved by locating the outlet opening at the lowest point on the hollow space in the operating position, where sand or the like will collect, for example, and can be flushed away. The supply or inlet opening in this design is advantageously located opposite the outlet opening, at the highest point on the hollow space.
In particularly preferred embodiments, the main seal includes two rings, associated respectively with the shaft and the sealed housing, which are pressed together at facing polished sealing surfaces which rub against one another during rotation of the shaft. In this arrangement the pressurized separating medium supports the sealing action by pressing the rings together. In certain preferred embodiments the rings are each provided with an angular cross-section and comprise a sealing surface on the free side of the edges which face one another. In certain especially preferred embodiments, the rings are forced together by respective elastically deformable sealing members of rubber or perbunan pressed against the same, said deformable sealing members being supported in a tight fitting manner against a flange mounted on the shaft and a collar projecting from the housing. These last mentioned features contribute to increased sealing action of the main seal.
Preferred embodiments are contemplated which include as an auxiliary seal, a sealing ring mounted in a through opening for the shaft and abutting the surface of the shaft. This arrangement lends itself to not impeding the desired escape of a portion of the separating medium through the auxiliary seal.
In certain preferred embodiments, the separating medium is compressed air which is advantageously produced by a pump, said pump being driven by the shaft to be sealed. In particular, when compressed air is used, no environmental pollution can occur although the separating medium continuously escapes to the outside through the space between the auxiliary seal and the outlet opening. The invention has also the advantage that polluted water and impurities such as sand or the like which have penetrated between the seals into the chamber during operating pauses, are immediately flushed out of the chamber at the beginning of a new operating phase through the outlet openings, and have no opportunity to have a harmful effect upon the sealing action of the main seal.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which show, for purposes of illustration only, a single embodiment in accordance with the present invention.